Influence of Amphiphilic Plasticizer on Thermoplastic Starch Films

Abstract

Different combinations of hydrophilic (malic acid and water) and amphiphilic (isoleucine and butyric acid) plasticizers were studied in the production of thermoplastic starch (TPS) powders and T-bones from corn starch. Spray drying was used to produce TPS powder followed by compression molding for development of T-bones. Amphiphilic plasticizers were used for better control over rate of moisture uptake and compatible mechanical properties in terms of tensile strength and elongation at break. All powder samples had an irregular and shrivelled morphology. In all combinations containing isoleucine, this additive exuded from the starch matrix and re-crystallized during spray drying, resulting in hollow particles. Rate of retrogradation and nature of freshly prepared powder were studied by XRD. Formulated samples inhibited the retrogradation of starch till 7th day and the nature of samples was amorphous due to spray drying except isoleucine plasticized and co-plasticized samples. FTIR was performed to investigate the better insight of the functional groups and interaction of plasticizers and starch matrix. Thermal stability was analyzed by TGA and DTGA curves of the samples. The crystallinity and moisture sensitivity of freshly prepared films depended on the amphiphilic plasticizer content in the plasticizer formulation. Increasing the content led to a decrease in moisture absorption. Isoleucine formulated films showed the best tensile strength, whereas malic acid-rich ones showed better strain at break values. At a relative humidity (RH) of 50%, the rate of retrogradation was low, but rate of it increased with increase in malic acid contents.